To a considerable extent, the various requirements which are involved in the mixing operations of commercial bakeries are also encountered in other food-processing and/or commercial and industrial activities, although the difficulties and obstacles present in the baking art often exceed those present in other fields.
For example, in the mixing of different baking doughs the requirement for achieving complete and substantially uniform dispersion of different materials, such as dry particulate matter, throughout the mix is more apt to be merely the beginning requirement rather than the ultimate one. For example, the recipes for different baked products often call for specific sequences of ingredient addition, with continuous mixing being carried out so that the addition of each different component technically produces a different mixture at a different point in time, and each such mixture is a prerequisite for the addition of the next ensuing ingredient. At the same time, baking doughs involve the physical chemistry of hydration, since they typically combine dry ingredients with various different liquid ingredients of widely-varying viscosities (e.g. from water to various oils, etc.), as well as utilizing various pastelike materials such as solid shortenings and the like, all of whose mixing characteristics differ very substantially from one another. Furthermore, baking often involves other requirements such as the need to "cream" ingredient mixtures by uniformly dispersing wet and dry ingredients and then working the resulting mix so as to incorporate air into it, as well as the requirement for "developing" dough, which involves plastic deformation of a hydrated dough mass, frequently including the need for substantial amounts of shearing or kneading of the dough mass by the mixer blades.
Generally speaking, food mixers are predominantly of the "horizontal" type, i.e., having agitators which rotate about a horizontally-disposed axis, although there are also various vertical mixers and special purpose devices. As will be understood, commercial food and/or bakery-product mixers operate on dough masses of the same general type as those encountered in home baking where mixers are usually of the vertical type, but the need for quantity and speed are substantially different in commercial operations, and this substantially exacerbates the degree of difficulty in meeting functional requirements as well as the significance of power consumption and the importance of speed. Thus, a mixer which performs well in the home environment may very well not do so in the commercial environment, but a mixer which performs well in the commercial environment is practically assured of functional acceptability, and probably of functional superiority, in other environments.
In the past, the predominating type of horizontal commercial mixer utilized one or more agitator elements having long, thin mixer blades which were bent into a helically-curving, longitudinally twisted shape. Typically, such prior agitator structures had a pair of such helical blades, each extending longitudinally along approximately half the length of the agitator but disposed on opposite sides thereof and located along different axial portions, i.e., each blade extending generally from an opposite end of the agitator and toward its midsection. In such agitators, a radially-extending cross arm located generally centrally of the structure is used to interconnect and reinforce the two opposite helically-curved mixing blades because the latter must of necessity have thin cross sections and are comparatively weak. Because of this structural weakness, such agitators had to have a rigid center drive shaft disposed along the axis of rotation, which supported and rotatably drove the twisted, helical mixer blade sections during mixing activity.
Agitators of the type just described have become an industry standard over the many, many years in which they have been used, even to the extent of being taken for granted and thus foreclosing objective evaluation of their performance. In fact, while it has to a large extent been presumed that mixers utilizing such agitators provided desirable or even optimum results, the present inventors have determined that such is not always, or even usually, the actual result, and that on the contrary such agitators provide a great many areas of defective performance, depending upon the specifics of the mixing task involved, such as the type of media to be mixed, amount of development required, desired speed of the performance, etc. In addition, it is not unusual to experience torsional failure in such agitators, due to the inherent structural weakness noted above, at which time the helical blades become twisted and bent, in effect destroying the agitator.
In addition, the previously predominating type of agitator structure, as described above, also inevitably involves the very serious disadvantage of having a high degree of manufacturing difficulty, resulting in the near impossibility of precise duplication. That is, in order to obtain the helically-curving shape, the mixing blades of such agitators had to be formed from comparatively thin elongated sections of metallic plate stock, which could be bent into generally helical configuration by complex processes, usually involving hammering and forging, etc. In fact, this type of blade actually involved a double curvature, which incorporates a twisting moment. Such a structure inevitably requires substantial individual shaping steps and considerable custom work, machining, etc. Furthermore, while such a complex shape is producible by casting processes, this involves very substantial expense and, furthermore, also requires considerable finishing machining, in order to obtain the required final dimensions and shaping. Of course, manufacturing of such agitators also involve the requirement for mounting the curving, twisting, helical mixing blades upon the center support shaft, and rigidly securing the same thereto so that they may withstand the demanding structural requirements encountered in actual use.
Due to these extensive fabrication difficulties, agitators of the type described above could never be produced as efficiently and economically as desired, and each such twisted helical blade is not likely to be identical to the next, resulting in substantial difficulty in producing operationally-satisfactory mixers having multiple agitators. Additionally, these fabrication and design problems kept the manufacturers involved from developing an agitator structure which was sufficiently strong to eliminate the center support shaft, even though such shafts present substantial operational disadvantage because they inherently interfere with desirable mixing flow patterns and introduce "dead zones" in the mixer interior. Also, such center shafts tend to promote build-up of the mix media along them, and thus introduce cleaning problems.